Method for comminuting solid synthetic resinous materials



ly .1961 H. D. GLENTON ETAL 2,993,400

METHOD FOR COMMINUTING SOLID SYNTHETIC RESINOUS MATERIALS Filed June 7,1957 I'll 1 mm, QM M y 1961 H. D. GLIENTON ET AL 2,993,400

METHOD FOR COMMINUTING soun SYNTHETIC RESINOUS MATERIALS Filed June 7,1957 3 Sheets-Sheet 2 no 5 (b) HTTOR/V'KS Jon/v M4 osr PHI/"P5 ByaWWIMWHEW/7r D4 :00 Gas/V7100 y 1961 H. b. GLENTON ET AL 2,993,400

METHOD FOR COMMINUTING sour; SYNTHETIC RESINOUS MATERIALS Filed June 7,1957 .5 Sheets-Sheet 3 FIGS by M Ma m 2,993,400 METHOD FOR COMMINUTIN GSOLID SYNTHETIC RESINOUS MATERIALS Henry David Glenton, Poulton, nearBlackpool, and

John Wildey Phipps, High Welwyn, England, assignors to Imperial ChemicalIndustries Limited, London, England, a corporation of Great BritainFiled l'une 7, 1957, Ser. No. 664,262 4 Claims. (Cl. 83-45) Thisinvention relates to a method and apparatus for comminuting solidsynthetic resinous materials in sheet or strip form.

Many proposals have been made for converting these materials into asuitable physical form for use in moulding and like operations. Forexample, it has been suggested that particles of the required shape andsize may conveniently be produced by cutting a sheet along a serratedline and then making a second serrated cut spaced back from the first.However, it has been found that this method is not wholly successful,particularly when the material of the sheet is soft, as there is atendency for it to be squeezed between the cutting edges, and instead ofa number of separate particles resulting these are connected together bythin threads or webs.

In order to overcome this disadvantage, a method of comminuting sheet orstrip of solid synthetic resinous material (hereinafter referred to assheet) has been proposed which comprises advancing sheet over a table(a) towards a stationary serrated knife which co-operates with at leasta pair of moving serrated knives, (b) along the line of one of the sidesof the serrations on the stationary knife and (c) at a rate not greaterthan half that required to advance it the length of said side during theinterval between cuts by said moving knives, one of said moving knivescutting the sheet protruding over every alternate indentation of saidstationary knife and the following moving knife cutting the sheetprotruding over every other alternate indentation of said stationaryknife.

The object of the present invention is to provide an improved method andapparatus for comminuting sheets of solid synthetic resinous materialsto produce particles, in which (a) the cut particles do not tend to bereturned to the cutting edges and therefore do not tend to preventregularity of cutting; (b) sheets of said materials which are relativelysoft, e.g. plasticised polyvinyl chloride sheets, even at temperaturesabove normal, e.g. 40 C., are fed steadily to the cutting edges withoutpuckering, which may occur when they move over a table in a horizontaldirection, as previously proposed; (C) out particles of any desiredshape may be conveyed directly from the cutter in any direction relativeto the direction from which the sheet is supplied; (d) the working partsof the apparatus are fully accessible; (2) the apparatus occupies only asmall floor area; and (f) the apparatus is easily constructed.

In order that our invention shall be fully understood it is illustratedin respect of the attached drawings.

FIGURE 1 is a cross-sectional diagrammatic representation of a means forsupplying plasticised polyvinyl chloride composition sheet andcomminuting it by the method of our invention.

FIGURE 2(a) is a cross section of the serrated edge of a knife suitablefor use in our invention.

FIGURE 2(b) shows the same serrated edge of the stationary knife and,superimposed upon it, the leading edge of a sheet which has alreadyreceived a series of cuts in position ready to receive another out whichwill remove the portions marked X.

FIGURE 2(0) shows the same serrated edge of the rates Patent PatentedJuly 25, 1961 stationary knife and, superimposed upon it, the leadingedge of the same sheet moved into position for the next cut which willremove the portions marked Y.

FIGURES 2(d)' and 2(e) correspond to FIGURES 2(1)) and 2(c) respectivelybut the direction of movement of the sheet (as indicated by the arrow)is different.

FIGURES 3(a) and 3(b) show two successive positions of the leading edgeof a sheet prior to cutting, superimposed on a stationary knife havingteeth of a different shape from those illustrated in FIGURES 2(a) to2(a).

FIGURES 4(a) and 4(b) show two successive positions of the leading edgeof a sheet prior to cutting, superimposed on a stationary knife havingteeth of yet another shape.

FIGURE 5 is an elevational view of a cutter of our invention with itshood on the stationary knife side removed;

FIGURES 6 and 7 are elevation section views taken in the region adjacentthe stationary knives and the moving knives; and,

FIGURE 8 is an enlarged fragmentary view of the rotor in FIGURE 5.

In FIGURE 1, 1 and 1 are counter rotating rollers upon which plasticizedpolyvinyl chloride composition 2, is sheeted. 3 is a knife for cutting anarrow sheet 4, therefrom. This sheet is passed through a cooling waterbath 5, and is moved by rollers 6, 7, 7' and 8, vertically downwardspast stationary knife S, to rotor 19, which rotates and carries fourmoving knives 11, which cooperate with stationary knife 9, comminutingthe sheet, and throwing the particles formed into hood 12, by means ofwhich they are conveyed to drum 13. It will be appreciated that the hood12, may lead to a duct which conveys the particles to drum 13, which maybe in the line in which the sheet is fed or on either side of this linewithout any costly modification of the installation. It will also beappreciated that space occupied by the cutting device may be minimizedby placing the stationary knife on the side of the sheet from which ithas been supplied and operating the moving knives so as to throw theparticles in the direction from which the sheet has been supplied.Furthermore, the cutting equipment is readily accessible on all sidesfor cleaning by detaching its hood, and also the means for moving thesheet to the knives is simple.

In FIGURES 2(b) and 2(c), the sheet is moved in the direction of one ofthe sides of the teeth of a station ary knife, and its leading edge isrepresented by 20 and 21 in the two positions prior to successive cuts.

In FIGURES 2(d) and 2(e), the sheet is moved at an angle to the samesides of the teeth with the result that the tips of the teeth areexposed at every cut in order to avoid the possibility of formingprotuberances on the particles cut. The leading edge of the sheet isrepresented by 22 and 23 in the two positions prior to successive cuts.

In FIGURES 3(a) and 3(b), the sheet is again moved at an angle to one ofthe sides of the teeth of a different stationary knife and its leadingedge is represented by 30 and 31 in the two positions prior tosuccessive cuts. In these figures, it will be noted the sides of theteeth are of unequal length.

In FIGURES 4(a) and 4(b) one of the sides of the teeth of the stationaryknife makes an angle to the normal to the general line of cutting andthe sheet is fed along this normal. The leading edge of the sheet isrepresented by 40 and 41 in the two positions prior to successive cuts.Particles having a diamond-shaped cross-section are produced in thisway.

In FIGURE 5, 4 is the sheet of solid synthetic resinous material movedvertically downwards by rollers 7 and 8,

3 past stationary knife 9, to rotor 10, carrying four moving knives ll.12 is the hood for the cutter which has been partially removed for thepurpose of this illustration. 13 is a drum in which the particlesproduced are collected and 14 is the motor driving the rotor 10.

FIGURES 6 and 7 show the manner in which successive teeth of the movingknives cooperate with the stationary knife. In these figures, 9represents the stationary knife, 11 represents one moving knife at theinstant of meshing with stationary knife 9, and 11 represents thefollowing moving knife at the instant of its meshing with stationaryknife 9.

FIGURE 8 is an enlarged fragmentary view of rotor 10 in FIGURE 5,wherein 11 and 11' have the same significance as above and 11 representsa third moving knife which cooperates with the stationary knife 9 afterknife 11. As shown, the teeth of knife 11 are staggered with respect tothose of knife 11 and the teeth of knife 11" are staggered with respectto those of knife 11. The tips of the teeth of knife 11 are indicated inFIGURE 8 by the letters T, T.

In accordance with the present invention, we prefer to feed the sheet tothe serrated cutting line in a substantially vertical direction in orderto minimize frictional drag between the sheet and the stationary knifeand to obtain the optimum removal of cut particles. We also prefer tofeed the sheet to the serrated cutting line at a rate less than halfthat required to advance the sheet, between successive cuts, along thelength of the projection of said side of the teeth of the stationaryknife in the direction of movement of the sheet. We also prefer to feedthe sheet to the serrated cutting line in a direction which subtends asmaller angle to a line joining the tips of the teeth of the stationaryknife than is subtended by the said side of the teeth of the stationaryknife. In these ways, we avoid a tendency for the softer syntheticresinous materials to be squeezed during cutting over the tips of theteeth of the stationary knife and appearing as thin protuberances on thecut particles produced. It is desirable to avoid these protuberances inorder to obtain free-flowing particles. Optimum free-flowingcharacteristics are obtained when the particles cut are substantiallycubes. Best conditions to obtain these are those of (a) right angledtips to the teeth of the cutting knives, (b) a rate of feed of one thirdof the projection of said sides on the direction of movement of thesheet, (6) the use of sheets having a thickness of two thirds of thelength of said sides and (d) a direction of movement of the sheet of2634 with the line of the tips of the teeth of the stationary knife. Asthere is ditficulty in practice in grinding right angled tips to thecutting knives, an approximation to these conditions is best used.

Particularly suitable synthetic resinous materials for use in thepresent invention are both the plasticized and unplasticizedthermoplastic materials, for example, those based on polymers andcopolymers of vinyl chloride, polyvinylidene chloride, celluloseacetate, polyamides, polythene, polystyrene, polymethyl methacrylate andthe resinous copolymers of butadiene with styrene and methylmethacrylate. For polymeric materials which are brittle at normaltemperatures it is desirable that the process of this invention isoperated at an elevated temperature.

Synthetic resinous materials are frequently obtained in sheet form bythe process of their manufacture or after they have been compounded withplasticizers, stabilizers, pigments, etc. For example, a polyamide suchas polyhexamethylene adipamide is normally extruded in the molten statethrough a slot at the bottom of the autoclave in which it has beenpolymerized and quenched in contact with a metal drum, thus forming athin sheet of narrow width. Various other polymers such as polyvinylchloride are normally mixed with plasticizers etc., in internal mixersof the Banbury type, and the mixing is completed on heated rolls fromwhich narrow sheets are removed by means of suitably placed knives.Before such sheets can be comminuted they should be cooled to the solidstate, e.g. by passing them through a bath of cooling liquid. We havefound that the sheets used in the present invention may be in aheat-softened condition and that intensive cooling after theirpreparation is seldom necessary. This results in an appreciable savingin capital and operating costs.

We claim:

1. Method of forming diced particles of solid synthetic resinousmaterial comprising the steps of: passing heated synthetic solidresinous material between a first pair of mating rollers to form thematerial into a continuous sheet; passing the sheet through a coolingzone to lower the temperature thereof to a predetermined value; thencefeeding the sheet of material while still in a heat softened conditionpast cooperating guide rollers in a vertically downward direction to aposition adjacent a downwardly facing stationary serrated cutting edge,the direction of feed being substantially coincident with one set ofcorresponding sides of the serrations of said cutting edge, maintainingthe sheet substantially free from crosssectional irregularities whollyby the action of the weight of the downwardly fed material; rotating acutter having first and second knives extending therefrom in cooperativeengagement with said serrated cutting edge in a manner to successivelycut the sheet protruding over every alternate indentation of saidcutting edge by the intermeshing teeth of said moving first knife andthen cutting the sheet protruding over every other indentation of saidcutting edge by the intermeshing action of said second moving knife,while feeding the sheet relative to said cutting edge at a rate notexceeding that required to advance the sheet one-half the length of saidserration sides between successive cuts, whereby the sheet is cut intodiced particles.

2. Method of forming diced particles of solid synthetic resinousmaterial comprising the steps of: passing heated synthetic solidresinous material between a first pair of mating rollers to form thematerial into a continuous sheet; passing the sheet through a coolingZone to lower the temperature thereof to a predetermined value; thencefeeding the sheet of material while still in a heat softened conditionpast cooperating guide rollers in a vertically downward direction to aposition adjacent a downwardly facing stationary serrated cutting edge,the direction of feed subtending a slightly smaller angle to a linejoining the tips of the serrated cutting edge, than is subtended by oneset of corresponding sides of the serrated cutting edge to the linejoining the tips of the serrated cutting edge, maintaining the sheetsubstantially free from crosssectional irregularities wholly by theaction of the weight of the downwardly fed material; rotating a cutterhaving first and second knives therefrom in cooperative engagement withsaid serrated cutting edge in a manner to successively cut the sheetprotruding over every alternate indentation of said cutting edge by theintermeshing teeth of said moving first knife and then cutting the sheetprotruding over every other indentation of said cutting edge by theintermeshing action of said second moving knife, while feeding the sheetrelative to said cutting edge at a rate not exceeding that required toadvance the sheet onehalf the length of said serration sides betweensuccessive cuts, whereby the sheet is cut into diced particles.

3. A method according to claim 1, in which the sides of said serrationsdefine teeth having right angled tips, the rate of feed of said sheetrelative to said cutting edge is about one third that required toadvance the sheet the length of said one set of serration sides betweensuccessive cuts, and the thickness of said material sheet is about twothirds the length of said one set of serration sides.

4. A method according to claim 1, in which the sheet comprises aplasticised polyvinyl chloride composition.

(References on following page) References Cited in the file 01 thispatent UNITED STATES PATENTS Bristol Dec. 9, 1899 Gangloff July 28, 19315 Matthews Nov. 11, 1941 Jehle Nov. 30, 1943 6 Gibby Apr. 21, 1953Kubodera July 9, 1957 Quinsey Nov. 12, 1957 FOREIGN PATENTS GreatBritain Dec. 31, 1952 France Jan. 21, 1957

